You know that moving every day is good for you: exercise helps lower blood sugar and control weight, among many other health benefits. But when it comes to determining what the best time to exercise is, it seems as though there are as many opinions out there as there are different diets. You want to exercise to improve or maintain your health, but maybe you don’t want to wake up at 5 a.m. to get in your early morning workout, or stay up until midnight so you can reap the benefits of evening exercise.

Don’t worry, things don’t have to be that difficult; doctors agree that the benefits of exercise at any time of day outweigh any potential advantages of exercising at a specific time of day. Let’s dig into what the science says (or not) about exercise timing and metabolic health.

The connection between exercise and metabolic health

Despite the various different scientific observations around exercise timing, the evidence is crystal clear on one thing: regular physical activity is a crucial component of blood glucose management and cardiovascular health: 

• Exercise can reduce the risk for type 2 diabetes by up to 50%.

• Exercise can be more beneficial than medication for some individuals with prediabetes or T2D. For example, in people with obesity or in people younger than 60, diet and exercise interventions can be more successful than Metformin (the most commonly prescribed drug for blood sugar control).

• Muscle strengthening activities have been associated with a lower risk for both diabetes and cardiovascular disease (CVD).

According to the American Diabetes Association, people with diabetes are twice as likely to have CVD than people without diabetes — and CVD is the number one killer of people with diabetes. Thus, exercise, through blood glucose control and positive effects on the cardiovascular system, delivers a one-two punch of health benefits for individuals with diabetes or prediabetes. And the good news is that both cardiovascular and muscle strengthening activities come with benefits, so you can choose the type of exercise you like best rather than forcing yourself to do something you don’t enjoy just because you think it's good for you.

The circadian rhythm and blood sugar and weight loss

Research on exercise timing is rooted in our recognition that the body’s circadian system — our internal molecular clock — has an impact on a number of physiological changes, from body temperature to hormone levels to muscular strength. Alterations in sleep or eating habits can severely impact your circadian rhythm, which can lead to serious consequences such as obesity, blood sugar dysregulation and even an increased risk for heart disease. Several studies have connected the circadian rhythm and meal timing with altered physiological parameters that also play a role in diabetes:

• Meal timing altered both the natural circadian clock and blood glucose levels in men without impacting appetite or sleep.

• Research suggests meal timing could beneficially impact weight and glucose metabolism.

• Late dinners have been associated with glucose intolerance.

Given these existing studies and the variability in exercise-induced weight loss, scientists have begun to look beyond what you should eat before and after a workout and toward the potential relevance of exercise timing. However, quality research in this area is scant, and the answer to the question, “When is the best time of day to work out for metabolic health?” isn’t so clear-cut. Let’s break it down.

Exercising in the morning or night: which is better?

The main reason why the research around when to exercise is so confusing is because so many factors can impact the effects of exercise (and therefore, exercise timing): 

• Gender:
• In a recent study published in the journal Diabetes Care, cardiorespiratory fitness  in a group of men with T2D increased with morning exercise, but for women the optimal fitness level appeared higher after evening exercise.

• Meal timing:
• Increased fat burning and weight loss in obese men was associated with morning exercise routines, but only when breakfast was consumed after working out.

• Health goals: 
• In a study published in the journal Diabetologia, early-evening training was superior to morning training for managing blood sugar and improving fat metabolism in a small cohort of overweight men at risk for diabetes.
• Similarly, high-intensity interval training sessions helped manage blood sugar in men with T2D when the sessions were performed in the afternoon; (morning sessions actually spiked blood sugar levels).
• In a study published in the International Journal of Obesity, weight loss was greater in men and women engaging in multiple moderate to vigorous morning aerobic exercise sessions than for individuals engaged in multiple evening sessions.
• A recent review found that blood glucose and lipemia (the concentration of emulsified fat in blood) are both improved in individuals with T2D after evening exercise, but not morning exercise.
• Insulin sensitivity and fat loss were improved after afternoon exercise in a small cohort of men at risk for T2D.

Importantly, many of these studies have been performed on people of only one gender, or in very small numbers of individuals and over short periods of time, making it difficult to draw meaningful, generalizable conclusions on the impact of exercise timing on metabolic health.

What about sleep?

You’ve probably noticed that many of the studies we’ve discussed suggest that evening exercise might be the way to go if you’re hoping to have better control over your blood glucose levels (at least if you’re a man — most of these studies were done in men only). But, you might ask, what about the impact of late exercise on sleep? After all, poor sleep quality has been associated with a higher risk of diabetes, so wouldn’t that risk outweigh any potential benefits associated with exercising later in the day?

The fact is, research in this area is inconclusive, too. If evening exercise works better for you, there are simple steps you can take to ensure you still get a good night’s sleep:

• Taking a cool shower before bed to lower your core body temperature;
• Keeping your bedroom at 65-68 degrees; and
• Finishing your last meal at least 2 hours before going to bed to minimize sleep disturbances.

Key Takeaways

So, when is the best time to exercise for metabolic health? Research on exercise timing and metabolic health remains inconclusive, but doctors all seem to agree on one thing: getting exercise every day, no matter when you do it, is vitally important for your health. While in the future research might elucidate meaningful connections between exercise timing and metabolic health, for now the best thing you can do is pick an exercise plan that is fun and easy for you to adhere to. Like diets, exercise plans will only work if they work for you — so reap the benefits, morning and/or night!